Cisco MDS 9000 Family Configuration Guide, Release 1.3 (from Release 1.3(1) through Release 1.3(6))
Configuring Trunking

Table Of Contents

Configuring Trunking

About Trunking

About the Trunking Protocol

Enabling or Disabling the Trunking Protocol

Trunk Mode Configuration

Configuring the Trunk Mode

Configuring Trunk-Allowed VSAN List

Configuring an Allowed List of VSANs

Trunking Configuration Guidelines

Displaying Trunking Information

Default Settings


Configuring Trunking


This chapter describes the trunking feature provided in Cisco MDS 9000 switches. It includes the following sections:

About Trunking

About the Trunking Protocol

Trunk Mode Configuration

Configuring Trunk-Allowed VSAN List

Trunking Configuration Guidelines

Displaying Trunking Information

Default Settings

About Trunking

Trunking, also known as VSAN trunking, is a feature specific to switches in the Cisco MDS 9000 Family. Trunking enables interconnect ports to transmit and receive frames in more than one VSAN, over the same physical link, using Extended ISL (EISL) frame format (see Figure 11-1).

Figure 11-1 Trunking

The trunking feature includes the following restrictions:

Trunking configurations are only applicable to E ports. If trunk mode is enabled in an E port and that port becomes operational as a trunking E port, it is referred to as a TE port.

The trunk-allowed VSANs configured for TE ports are used by the trunking protocol to determine the allowed-active VSANs in which frames can be received or transmitted.

If a trunking enabled E port is connected to a third-party switch, the trunking protocol ensures seamless operation as an E port.

About the Trunking Protocol

The trunking protocol is important for E-port and TE-port operations. It supports the following:

Dynamic negotiation of operational trunk mode.

Selection of a common set of trunk-allowed VSANs.

Detection of a VSAN mismatch across an ISL.

By default, the trunking protocol is enabled. If the trunking protocol is disabled on a switch, no port on that switch can apply new trunk configurations. Existing trunk configurations are not affected—the TE port continues to function in trunk mode, but only supports traffic in VSANs that it negotiated with previously (when the trunking protocol was enabled). Also, other switches that are directly connected to this switch are similarly affected on the connected interfaces. In some cases, you may need to merge traffic from different port VSANs across a non-trunking ISL. If so, disable the trunking protocol.


Tip To avoid inconsistent configurations, shut all E ports before enabling or disabling the trunking protocol.


Enabling or Disabling the Trunking Protocol

To enable or disable the trunking protocol, follow these steps:

 
Command
Purpose

Step 1 

switch# config t

Enters configuration mode.

Step 2 

switch(config)# no trunk protocol enable
switch(config)# 

Disables the trunking protocol.

switch(config)# trunk protocol enable
switch(config)#

Enables trunking protocol (default).

Trunk Mode Configuration

By default, the trunk mode is enabled in all Fibre Channel interfaces. However, the trunk mode configuration takes effect only in E-port mode. You can configure the trunk mode as on (enabled), off (disabled), or auto (automatic). The default trunk mode is on. The trunk mode configuration at the two ends of an ISL, between two switches, determine the resulting trunking state of the link and the port modes at both ends (see Table 11-1).

Table 11-1 Trunk Mode Status Between Switches 

Your Trunk Mode Configuration
Resulting State and Port Mode
Switch 1
Switch 2
Trunking State
Port Mode

On

Auto or on

Trunking (EISL)

TE port

Off

Auto, on, or off

No trunking (ISL)

E port

Auto

Auto

No trunking (ISL)

E port



Note When connected to a third-party switch, the trunk mode configuration has no effect—the ISL is always in a trunking disabled state.


Configuring the Trunk Mode

To configure the trunk mode, follow these steps:

 
Command
Purpose

Step 1 

switch# config t

Enters configuration mode.

Step 2 

switch(config)# interface fc1/1
switch(config-if)# 

Configures the specified interface.

Step 3 

switch(config-if)# switchport trunk mode on

Enables the trunk mode for the specified interface.

switch(config-if)# switchport trunk mode off

Disables the trunk mode for the specified interface.

switch(config-if)# switchport trunk mode auto

Configures the trunk mode for the specified interface. The auto option provides automatic sensing for the interface.

Configuring Trunk-Allowed VSAN List

Each Fibre Channel interface has an associated trunk-allowed VSAN list. In TE-port mode, frames are transmitted and received in one or more VSANs specified in this list. By default, the VSAN range (1 through 4093) is included in the trunk-allowed list.

The common set of VSANs that are configured and active in the switch are included in the trunk-allowed VSAN list for an interface, and they are called allowed-active VSANs. The trunking protocol uses the list of allowed-active VSANs at the two ends of an ISL to determine the list of operational VSANs in which traffic is allowed.

In Figure 11-2, switch 1 has VSANs 1 through 5, switch 2 has VSANs 1 through 3, and switch 3 has VSANs 1, 2, 4, and 5 with a default configuration of trunk-allowed VSANs. All VSANs configured in all three switches are allowed-active. However, only the common set of allowed-active VSANs at the ends of the ISL become operational as shown in Figure 11-2.

Figure 11-2 Default Allowed-Active VSAN Configuration

You can configure a select set of VSANs (from the allowed-active list) to control access to the VSANs specified in a trunking ISL.

Using Figure 11-2 as an example, you can configure the list of allowed VSANs on a per-interface basis (see Figure 11-3). For example, if VSANs 2 and 4 are removed from the allowed VSAN list of ISLs connecting to switch 1, the operational allowed list of VSANs for each ISL would be as follows:

The ISL between switch 1 and switch 2 shall include VSAN 1 and VSAN 3.

The ISL between switch 2 and switch 3 shall include VSAN 1 and VSAN 2.

The ISL between switch 3 and switch 1 shall include VSAN 1, 2, and 5.

Consequently, VSAN 2 can only be routed from switch 1 through switch 3 to switch 2.

Figure 11-3 Operational and Allowed VSAN Configuration

Configuring an Allowed List of VSANs

To configure an allowed-active list of VSANs for an interface, follow these steps:

 
Command
Purpose

Step 1 

switch# config t

Enters configuration mode.

Step 2 

switch(config)# interface fc1/1
switch(config-if)# 

Configures the specified interface.

Step 3 

switch(config-if)# switchport trunk allowed vsan 2-4

Changes the allowed list for the specified VSANs.

switch(config-if)# switchport trunk allowed vsan add 5
updated trunking membership

Expands the specified VSAN (5) to the new allowed list.

switch(config-if)# no switchport trunk allowed vsan 2-4

Deletes VSANs 2, 3, and 4.

switch(config-if)# no switchport trunk allowed vsan add 5

Deletes the expanded allowed list.

Trunking Configuration Guidelines

If you misconfigure VSAN configurations across E ports, you could face consequences such as merging the traffic in two VSANs (thus causing both VSANs to mismatch). The trunking protocol validates the VSAN interfaces at both ends of an ISL to avoid VSANs merging (see Figure 11-4).

Figure 11-4 VSAN Mismatch

In this example, the trunking protocol detects potential VSAN merging and isolates the ports involved.

The trunking protocol cannot detect merging of VSANs when a third-party switch is placed in between two Cisco MDS 9000 Family switches (see Figure 11-5).

Figure 11-5 Third-Party Switch VSAN Mismatch

VSANs 2 and 3 get effectively merged with overlapping entries in the name server and the zone applications. The Cisco MDS 9000 Fabric Manager helps detect such topologies (refer to the Cisco MDS 9000 Family Fabric Manager Configuration Guide).

Displaying Trunking Information

The show interface command is invoked from the EXEC mode and displays trunking configurations for a TE port. Without any arguments, this command displays the information for all of the configured interfaces in the switch. See Examples 11-1 to 11-3.

Example 11-1 Displays a Trunked Fibre Channel Interface

switch# show interface fc1/13
fc1/13 is trunking
    Hardware is Fibre Channel
    Port WWN is 20:0d:00:05:30:00:58:1e
    Peer port WWN is 20:0d:00:05:30:00:59:1e
    Admin port mode is auto, trunk mode is on
    Port mode is TE
    Port vsan is 1
    Speed is 2 Gbps
    Receive B2B Credit is 255
    Beacon is turned off
    Trunk vsans (admin allowed and active) (1)
    Trunk vsans (up)                       (1)
    Trunk vsans (isolated)                 ()
    Trunk vsans (initializing)             ()
    5 minutes input rate 0 bits/sec, 0 bytes/sec, 0 frames/sec
    5 minutes output rate 0 bits/sec, 0 bytes/sec, 0 frames/sec
      233996 frames input, 14154208 bytes, 0 discards
        0 CRC, 0 unknown class
        0 too long, 0 too short
      236 frames output, 13818044 bytes, 0 discards
      11 input OLS, 12 LRR, 10 NOS, 28 loop inits
      34 output OLS, 19 LRR, 17 NOS, 12 loop inits

Example 11-2 Displays the Trunking Protocol

switch# show trunk protocol
Trunk protocol is enabled

Example 11-3 Displays Per VSAN Information on Trunk Ports

switch# show interface trunk vsan 1-1000
fc3/1 is not trunking
...
fc3/7 is trunking
	Vsan 1000 is down (Isolation due to vsan not configured on peer)
...
fc3/10 is trunking
    Vsan 1 is up, FCID is 0x760001
    Vsan 2 is up, FCID is 0x6f0001

fc3/11 is trunking
    Belongs to port-channel 6
	Vsan 1 is up, FCID is 0xef0000
    Vsan 2 is up, FCID is 0xef0000
...
port-channel 6 is trunking
	Vsan 1 is up, FCID is 0xef0000
    Vsan 2 is up, FCID is 0xef0000

Default Settings

Table 11-2 lists the default settings for trunking parameters.

Table 11-2 Default Trunk Configuration Parameters 

Parameters
Default

Switch port trunk mode

On.

Allowed VSAN list

1 to 4093 user-defined VSAN IDs.

Trunking protocol

Enabled.